If you have Rick's Italy guidebook, you'll see his suggestions for restaurants in Manarola. Here are some restaurants from that book:
The vast majority of the town's restaurants (all of them decidedly touristy) are concentrated in the tight zone between Piazza Capellini and the harbor. While these are mostly interchangeable, the Scorza family works hard at Trattoria il Porticciolo (€7-10 pastas, €9-18 secondi, Thu-Tue 7:30-23:30, closed Wed, Via Birolli 92, tel. 0187-920-083). At the harborfront itself, Marina Piccola is famous for great views, lousy service, and gouging naive tourists.
Ristorante di Aristide, right on Piazza Capellini, offers trendy atmosphere and a pleasant, less claustrophobic outdoor setting, with a view of budding soccer stars rather than harborfront glitz (€8-12 pastas, €10-19 secondi). Down the stairs, at the bottom of the main street, their simpler café has indoor and streetside seating and a simpler menu (€5-7 pizzas, sandwiches, and salads; both open Tue-Sun 8:00-22:30, closed Mon, Via Discovolo 290, tel. 0187-920-000).
Via Discovolo, the main street climbing up through town from Piazza Capellini to the church, is lined with simpler places, including a popular gelateria and some small grocery stores where you can browse for a picnic.
Up at the very top of town, in the residential zone above the church, dining options are sparse, but the one place that's here is a good one: Trattoria dal Billy offers both good food and impressive views over the valley. With Edoardo and Enrico’s black pasta with seafood and squid ink, green pasta with artichokes, mixed seafood starters, and homemade desserts, many find it worth the climb. Dinner reservations are a must (€8-12 pastas, €13-20 secondi, generally daily 8:00-15:00 & 19:00-23:30, closed Thu, Via Aldo Rollandi 122, tel. 0187-920-628).
I hope this helps some.